Category Archives: How-to’s

How to Compute Compression Ratio, Head Volume, Dish, etc.

I am planning a motor build for Project Domino. There is nothing worse than spending money on parts to only figure out you ordered the wrong thing. In this particular case, I wanted to make sure I ordered the right pistons the first time to achieve a reasonable compression ratio for pump gas.

Compression Ratio

I want to get to the basic math without going too deeply into how engines work, so I will provide a brief term overview. I will use Domino’s EJ207 for an example.

Computing Displacement Volume

Displacement/Swept Volume refers the volume displaced from the piston moving up (top dead center) and down (bottom dead center).

It is computed by the surface area of the piston times the stroke of the piston, times the number of cylinders.

displacement per cylinder = π * (bore / 2)² * stroke

total displacement = π * (bore / 2)² * stroke * num_pistons

eg. EJ207’s displacement = π * (92mm / 2 )² * 75mm * 4 = 1994cc

Computing Compressed Volume

Compressed/cleared volume refers to the volume between the surface of the top of the piston when at top dead center and the top of the cylinder head.

compressed_volume = piston_dish + ((bore / 2)² * (piston_deck + gasket_thickness)) * head_volume

eg. EJ207 compressed volume = 6cc + ((92mm / 2 )² * (1.42mm + 0.6mm)) + 50cc = 69.5cc

Computing Compression Ratio

Engine compression is essentially taking the displaced volume and squishing it into the cleared or compressed volume as the piston travels from bottom dead center to top dead center. Compression ratio is therefore:

compression_ratio = (cylinder_displacement + compressed_volume) / compressed_volume

eg. EJ207 compression ratio = (498.5cc + 69.5cc) / 69.5cc = 8.2

Now What?

Now that you have the basic idea of how the compression works, how is it useful?

Given some fixed variables, you can figure out how to adjust the others to achieve a reasonable compression ratio.

Note: if you are not increasing the head volume, then the only way to change the compressed volume is to modify either the piston dish, piston deck, or gasket thickness. Ideally, you modify it with the piston dish for reasons I will not go into. Rods length can change the piston deck, so consider it a factor when selecting the pistons.

The main way to change displacement is modifying the bore and stroke. For EJs, 2.1 stroker is *roughly* a 92mm piston with a 79mm crank, a 2.34l destroker is a 75mm crank with 99mm pistons, a 2.6 stroker is a 83mm stroke with a 99mm pistons…etc.

Applied Math

I wanted to build a 2.36l destroker with +2mm long rods. I won’t go into all of the reasons, but the thrust of it is that I wanted more displacement while keeping somewhat in the high-revving spirit of the EJ207.

Computing displacement is easy, we already have all of the variables:

displacement = π * (100mm / 2 )² * 75mm * 4 = 2356cc

I know I want to hit a target compression ratio of somewhere around 8.5-9.0, we don’t have the compressed volume yet.

We need: piston dish, compute piston deck, and factor in gasket thickness. We will keep the head volume at 50cc. I also don’t want to order custom internals, so we will stick with Manley’s catalog.

The long rods are +2mm longer or ~132.5mm center to center. Destroker pistons made for standard rods have a compression distance of 32.6mm. To keep piston deck constant, and not have the piston sticking out of the block, we need that to be 2mm less. Pistons for 79mm cranks are 30.7, and 83mm cranks are 28.7mm. So, the 79mm crank pistons are good, or ~1.9mm less, which makes sense. The stroke difference is 4mm / 2 = 2mm. So, the new piston deck is 1.53mm to account for the 0.1mm difference.

Manley’s piston has a -17cc dish.

compressed volume = 17cc + ((100mm / 2 )² * (1.53mm + 0.6mm)) + 50cc = 72.3cc

Compression Ratio = ((2356cc / 4) + 72.3cc) / 72.3cc = 9.15

That is a little on the high side, so how could we hit a lower target? Basically by increasing the compressed volume. If we wanted to hit say 8.5, what would it have to be?

((2356cc / 4) + X) / X = 8.5
=>(8.5 * X) – X = 589
=> X = 589 / 7.5 = 78.5cc

Or, we’d need 6.2cc more compression volume to achieve a compression ratio of 8.5. This can be done with the head gasket, or finding another piston with more dish, or increasing the head volume.


I found this helpful table on NASIOC for EJ motors. Hit the source link if you want to see it on that site.

Source: Titter

Installation Guide for EJ fitment Steam Speed Turbochargers.

We are proud to announce  a simple installation guide that can be used on all EJ fitment vehicle.  We kept most of the description as generic as possible and high lighted the key steps in replacing your turbo. As stated in the video there may be differences in your exact application.  Below the video is the full transcript of the narration.

Full Transcript

Welcome to the installation video for EJ fitment steam speed turbo chargers.

  • Today we will be installing a steam speed stx67r-10 twin scroll on our version 8 ej207. This process can be applied to any EJ fitment vehicle or to these listed part numbers.
















  • Notice our vehicle is far from stock and what you see in the video may not match your vehicle. However, the key points of the process will be the same.
  • We begin by gaining clear access to the turbo. We removed the air filter and Mass Air Flow sensor housing and charge pipe at the turbo.
  • If you have a top mount inter cooler remove that from the throttle body and compressor outlet.
  • The silicon or plastic hoses may be stuck. Use brake clean to break the adhesion and carefully work the sealing edge with a hose pick. Take caution not to puncture or tare the hoses as this will lead to a boost leak later.
  • Next remove any heat shielding you may have installed. Whether that’s a turbo blanket such as the steam speed titanium or carbon fiver turbo blankets or bolted on stamped steel heat shields.
  • Next use a rust penetrator such as “wd40”, or “pb blaster” and soak the turbine housing bolts on the up and down pipe flanges. Allow them to soak for at least 15 to 20 minutes.
  • While the bolts soak, place a collection pan underneath the vehicle directly below the turbo and remove the coolant and oil lines connected to the CHRA portion of the turbo.
  • I suggest using hose clamps to minimize the amount of spilled coolant and coolant unnecessarily draining from the engine.
  • I also cap the coolant lines on the turbo to also minimize the mess.
  • Next you can begin to loosen and remove all the up and down pipe flange bolts.
  • Caution, these bolts can break if too rusted together. If this happens you will need to replace them.
  • When the flange bolts and nuts are removed disconnect the down pipe from its solid mounts on the side of the transmission. Up plug any oxygen sensors and move the down pipe from the vehicle.
  • Once the down pipe is clear loosen the compressor inlet pipe and maneuver it toward the front of the vehicle underneath the intake manifold until it is clear of the compressor housing.
  • Then you should be able to lift the turbo off the up pipe flange and oil drain tube.
  • Take caution with the oil drain tube as the hoses can stick and tension clamps can lose their tension over time and fall off while removing. The open oil drain will be exposed and can risk material falling into it.
  • Place the new and old turbo chargers on a work bench and note any comparable differences that may cause fitment issue or parts that may need to be transferred such as coolant lines or the oil drain tube.
  • Next you will see there are 3 studs provided with your new turbo. Place these in the corresponding locations compared to your previously removed turbo. Then tighten these studs with a 7mm open end wrench.
  • Apply thread sealant or thread tape to the oil feed line fitting on the back side of the cylinder head. This will be a hard line on AVCS equipped engines.
  • Then install the oil feed line.
  • Prep the up and down pipe flanges for new gaskets, remove any surface rust or grease and oil with a fine grade abrasive pad. Then place your new up pipe gasket on the flange.
  • Place your new steam speed STX turbo charger on to your up pipe flange. Remain aware of the oil drain tube alignment. If the drain tube is new it may be more difficult to slide onto the metal portion connected to the CHRA (center housing rotation assembly). You can apply a thin film of engine oil to the rubber drain tube to ease its fitment on to the metal portion. Then Place the tension clamps back into place.
  • Carefully guide your turbo inlet pipe onto the inlet of the compressor housing. On larger turbo’s this may be more difficult as the compressor inlet diameter may be larger than the diameter of your inlet pipe. Tighten the clamp, securing it to the compressor housing.
  • Begin to reinstall all the nuts and bolts securing the turbo to the up pipe. Be sure all nuts and bolts are in place before tightening all the way. Place your down pipe gasket on to the outlet flange and studs on the turbine housing. And guide the down pipe into place.
  • Then install the down pipe flange nuts and bolts. Again do not tighten until all bolts are in place.
  • Torque all up and down pipe bolts to 26 ft/lbs
  • Next apply thread sealant or tread tape to the oil feed line fitting on the top side of the CHRA.
  • Reconnect the coolant hoses and vacuum lines.
  • Carefully check each step on the installation to be sure nothing was missed or any hoses moved out of place.
  • Reinstall the charge pipe and air filter housing.
  • The most important step is priming the oil system. If this step is not performed eruptible damage will be done to the CHRA.
  • Disable the ignition system but either removing the crank sensor signal.
  • Crank the vehicle over for a minimum of 30 seconds.
  • Re connect the ignition system and start the car.
  • Allow the vehicle to idle for 15 to 20 minutes and reach operating temp slowly. Do not rev the engine.
  • Inspect your work for coolant or oil leaks at the fittings and hoses.
  • Be observant for a hiss noise of possible vacuum or intake leaks.
  • Once the vehicle has been thoroughly checked, let it cool and reinstall your heat shielding.
  • It is now imperative your vehicle is tuned by a trusted tuner using a chassis dynamometer.


Steam Turbo Install Instructions

SteamSpeed Logo

Download the PDF – Steam STX Turbo Installation Instructions

Steam STX Turbo Installation Instructions

Steam STX Turbochargers are manufactured with the highest quality components, equipment, and procedures as possible.  When installed, maintained, and operated correctly, these turbos can provide many years of reliable service.  Incorrect turbo installation can lead to premature turbo failure and voids the warranty.  Professional installation is recommended.

Pre-installation Checklist

  • Make sure the engine, oil, and cooling systems are healthy, clean, and in good working order.
  • If you’ve had an engine or turbo failure, make sure the root cause has been identified and addressed.
  • Change the engine oil with clean new oil and a new filter.
  • Make sure the pre-turbo intake and pre-turbo exhaust systems are free of foreign objects.
  • We recommend replacing the OEM oil feed line, but if you are reusing the stock line, make sure it is clean and unobstructed. We sell upgraded stainless steel oil feed lines at affordable prices to help our customers avoid oil starvation problems caused by clogged oil feed lines.
  • Ensure the crank case ventilation system is operating correctly.

Turbo Installation
1. Remove the old turbo. If you are unsure how to do this, refer to the service manual for the car.  Generally this involves these steps:
– Remove the down pipe.
– Remove the connected intercooler and/or intercooler piping connected to the turbo.
– Disconnect and temporarily clamp the turbo’s water lines.
– Disconnect the oil feed line. Note: take care to not crack or over bend the stock oil feed line if you intend to reuse it.
– Disconnect the vacuum line from the compressor housing (if applicable).
– Unbolt and remove the turbo from the up pipe. The oil return hose and clamps will be reused.
2. Install the new Steam STX turbo. Perform the turbo removal steps in reverse.  Note:
– Make sure all of the hoses and fittings are tightly clamped post install.
– Always replace old gaskets with new SteamSpeed gaskets or OEM gaskets.
– Make sure all flange surfaces are flat and clean before replacing the gaskets.
– Pre-turbo exhaust leaks and post-turbo boost leaks are the main cause for slow turbo spool up.
– Replace corroded or otherwise damaged hardware as needed.
– Use OEM torque specs.
3. Prime the turbo by cranking the engine without firing for at least 30-60 seconds. You can disable the ignition by removing the ignition fuse, or disconnecting the sparkplugs.  Skipping this step will lead to premature turbo failure and will void your warranty.
4. Start the engine and let it idle for at least 3-4 minutes. While the engine is idling, check for leaks, and if any are detected, stop the engine at once and fix the leak.
5. Stop the engine and recheck the engine oil level.
6. Enjoy boosting with your new Steam STX turbocharger!

SteamSpeed TECH: How to Preload a Wastegate Actuator

How does one correctly preload a turbocharger’s waste actuator?

We get asked this question often, so here is a little guide on how to correctly preload a turbo’s wastegate actuator.  In general, you adjust the preload according to the pressure of the spring that is in the actuator.  Most aftermarket turbos are set to 1.0 bar.  Actuators can be adjusted up or down ~+/- 0.1 bar of their spring pressure.  Our turbos come preloaded with 0.9-1.2 bar depending on the application.

Our adjustable actuators can take a number of different springs to achieve a wide range of preloads.  We also sell them separately as a retrofit for people with stock or other brands of turbos.  Extra springs if you already have our actuator.

1. Attach the actuator to the compressor housing.

Attach the waste gate actuator to the compressor housing
Attach the waste gate actuator to the compressor housing

2. Attach the actuator to the arm of the turbine housing’s flapper arm.  Note: do not insert the cotter pin yet to the flapper arm.

Attach the waste gate actuator to the turbine housing
Attach the waste gate actuator to the turbine housing

3. Attach a boost source to the barb on the waste gate actuator.   Pictured below is a custom made apparatus that connects to an air compressor.  We also sometimes use a reversible vacuum pump (one that can be reversed to make pressure as well as vacuum) and use that to apply the target pressure.

Apply a boost source on the actuator's barb
Apply a boost source on the actuator’s barb

4. Apply the target pressure which should match the spring that is inside.  Then, apply 0.1 bar of pressure more than the target.

Add pressure to the target boost level
Add pressure to the target boost level

5. Check the flapper’s gap.  It should be open around 0.10mm at 0.1 bar beyond the target preload.  We are using a 0.10mm gap feeler to check.  If you do not have a gap checker, you can get close by watching the flapper to move ever so slightly.

Check the flapper's gap
Check the flapper’s gap

6. If the gap was correct in step 5, go to step 7.  If the gap is not correct, you fine tune by adjusting the actuator rod.  Shorten the rod to add more preolad.  Lengthen the rod to decrease the preolad.  Repeat steps 2-6 until the preload is correct.

Adjusting the length of the actuator arm
Adjusting the length of the actuator arm

7. Reattach the cotter pin.  You turbo is now correctly adjusted.

All finished
All finished



What to Do When a Coolant Line Is Too Short

We have had questions of what to do if the OEM water lines are not long enough.  The short answer is to make a new water line.  It is simple to do and effective.  What you don’t want to do is to force your stock line to fit if it is not long enough.  In the worst case, it will crimp you line and prevent your turbo from being cooled correctly.

How do you make a new water line?

  1. Buy a length of antifreeze safe hose from your local auto part store.  Generally it is sold by the foot, and 12″ is plenty.  In our example, we used Gates 3/8″ fuel injection hose because it is the right diameter, and it works.
  2. Remove the old water line.
  3. Next determine how long to cut the new hose.  Put it in the engine bay and test fit the line.  Make it long enough such that the hose is not pinched and has a nice curve.  It doesn’t need to be too long such that it rubs against anything.
  4. Cut the hose to the correct length.
  5. Remove the sliver heat shielding off of the factory line.
  6. Put it on the newly cut line.
  7. Connect the new line with the heat shield onto the turbo and cylinder head.
  8. Ensure that the line is properly clamped on both ends.
  9. After starting the car for the first time, make sure there are no leaks.

Here is the finished product.  Note there are no kinks and we are reusing the OEM heat shielding.  We used common 3/8″ Gates fuel injector hose.

turbo water line
This is the finished product. We cut a new line that was approximately 2″ longer than the stock one. Note there are no kinks, and we are reusing the stock heat shielding from the OEM line.



How to Calculate a Turbo’s Trim



trim = inducer²/exducer² * 100

ex. take a TD05H-20g compressor wheel:
inducer diameter: 52.56mm
exducer diameter: 68.01mm
trim: ?

trim = (52.56mm)² / (68.01mm)² * 100
= 2762.5536 / 4625.3601 * 100
= 59.7…
~= 60

ex. take the turbine of a Garrett GTX2867R where Garrett doesn’t list the inducer diameter
inducer: ?
exducer: 53.8mm
trim : 76

76 = inducer²/(53.8mm)² * 100
=> 76 / 100 = inducer² / 2894.44mm²
=> .76 * 2894.44mm² = inducer²
=> inducer = sqrt(2199.7744mm²)
=? inducer = 46.9mm

I am getting turbo compressor surge; how do I fix it?

I am getting turbo compressor surge; how do I fix it?

There are at least two kinds of compressor surge:
1. the intake path is being too restrictive so the boost is hitting too much back pressure causing a surge
2. -or- the turbine/turbine housing is mismatched with the exhaust flow such that the exhaust is out flowing the compressor pushing it to the left of the surge line. You can see this at higher RPMs.

For #1:
– If having your throttle closed cause a surge or boost spike, then I think you blow off valve is not working correctly. Using a recirculating blow of valve is normally the best.
– if your BOV is working, then maybe there is a restriction in your intake path.

For #2:
– if you are getting boost creep, you could consider porting out the waste gage hole turbine section so that it is smooth a little bigger. Make sure the flapper still shuts it off completely when closed.
– you can also try a bigger hotside, or external wastegate
– a bit of compressor surge here may be acceptable

Guage Wiring Using the Clock Wiring Harness

Planning on adding some gauges to your WRX? There are several methods to get the proper voltage sources to get the job done, but just using the wiring harness for the clock is the simplest in my opinion. It has all of the voltage sources you need, and it is a great location.  This is especially if you are planning a gauge pod in the clock’s spot, or cluster bezel.  On my ’05, I personally used the SMY ClusterMaker Dual Gauge Pod 52mm that replaces the factory cluster bezel. I personally like keeping my clock and don’t favor the look of having the gauges on the a-pillar.

Here is the breakdown on the wiring harness for the clock:
Clock Wiring for Gauges

I spliced right into the wires I needed and soldered in the power harness for the the boost gauge I was installing.  Before buttoning everything back up, it is a good idea to make sure everything is working as expected.
Test fitting the bezel gage pod